Winme

My 2003 ML 270 CDI engine is surging (RPMs shuttle from 2500 to 2300) at 120 km/hr and AT never shifts down. I am suffering of this problem for more than 4 years and could not find remedy. I read lots of threads where people claim about same situation but never seen how the problem was resolved. Boost pressure in this regime is about 10 psi and slightly goes up and down as PRMs do. Just quick touch to accelerator makes the boost pressure jump to about 1 bar and surges disappear. 120 km/hr is kind of Bermuda triangle and Mercedes has left me alone with my mystery problem. tried AT oil replacement but helped for few weeks only. My regards to Mercedes community, Victor.

Dtpetrov

Hello guys, greetings from Bulgaria. I have exact the same problem with ml 270 year 2002. I've changed a lot of things, sensors etc., but the problem is still here. Please if someone solved it tell us what you do because i run out of ideas. I have tried every thing i can imagine. Thank you.

Winme

Hello Dtpetrov,
I also tried many things to cure engine surging/pompage problem: cut-out second catalyst (regret about it), replaced the first catalyst with a "good" one, replaced crank sensor, replaced throttle sensor (with an used but "good" one), replaced fuel rail with a later years OM612 one with a brand new pressure sensor and a pressure regulator valve (the later pressure regulator and sensor do not fit to the older rail), replaced HP pump plungers and valves - all this ended up with no improvement to engine surging.
I did an EGR valve delete using a signal emulator (thanks to our Polish friends for this emulator). EGR valve delete gave some improvement but after few months engine performance got even worse - surging got deeper and deeper, engine sound was very strange - as if it was calling for help! , with the engine surging (when riding uphill) I used to go to fourth and even to third gear (using tiptronic) and I never had more than 3000 rpms accompanied with severe surges again (gas pedal to the very floor!). I was sure I had fuel starvation - I inserted a pressure gauge in the fuel line from low pressure pump to the HP pump - I had no less that 2.9 bar at any load/any temperature but the engine was struggling anyway.
My mistake after EGR delete was that although I unplugged the EGR valve vac. transducer electrical connection, I never removed the vacuum tube from it - it occurred that de-energized transducer was leaking vacuum to the EGR valve pneumatic actuator making it stay slightly open all the time (which was very bad!). Ok, I removed vac. tubes - problems persisted. Now I know that if you are deleting the EGR you MUST insert a metal blank somewhere in exhaust gas to EGR valve passage. In closed position my EGR valve seat was passing exhaust gases - I removed the valve, submersed into the water and checked with a bike tire hand pump - EGR was bubbling "generously" at about 0.5 bar. I drilled the EGR valve nozzle next to the connector piece to the exhaust gases cooler, installed a fitting and measured exhaust pressure under load - it was up to 3 bar and this is normal! imagine how much dead gases were going to cylinders at full load! this was a main reason I had no more than 0.5 bar boost pressure by the beginning of surge and then no more than 0.7/0.8 bar at full throttle. I inserted an aluminum sheet blank gasket at the exhaust gas cooler inlet side (two of flange bolts to unscrew, easily accessible if you remove driver side wheel and a plastic fender liner). Now I have 1.1 - 1.2 bar boost pressure under heavy load - engine performance is much better.
Sorry for so long story about EGR and engine performance - slight surges (but much slighter) still were there!

I had a complex problem - with an engine and with ---- automatic transmission.
I replaced transmission fluid at about 165 000 km and there was 190 000 km on the clock when these surges started to really worry me. If you have a slight rpm surges at 120km/h ( 2480 - 2500rpm) and you have not replaced transmission fluid for a long time, you can be nearly sure the torque converter lock-up clutch is slipping at high load. This is no "fatal" transmission failure - fluid/filter change must cure the problem. If your W163 is first generation one, you may have a drain plug on the converter - then the full oil change is "one go" work. If W163 is a facelift one, it has no drain plug on converter. Only about four liters of fluid is possible to change at a time. Mercedes do not recommend transmission machined oil flush and oil change on higher mileage ones - flushing machine agitates sediments in the oil pan and you may encounter problems with hydraulic solenoid block. it is better to remove the oil pan, clean it, replace filter and partially change the oil (about a half of full amount). after a few hundred kilometers you can remove the pan again and drain next four liters of oil. (you will be able to drain only TWO liters of oil if just oil pan drain plug is removed, and that plug is a shame to Mercedes). You stop partial oil changes when you are happy with the color of drained ATF
There are many threads here om MB World how to replace 722.6 transmission oil and filter.
So far I have done partial oil change two times and transmission performs well. I am still not happy with the drained oil color, I am going to do next oil change.
I assume, transmission control module should see engine rpms STEADY decrease when the engine is loaded. But rpm surges, caused with lock-up clutch slippage fouls important input data to control module and prevents it to work properly - automatic transmission does not downshift.

This is all my "theory" and personal experience with a problem similar to yours,
I hope it helps you,
Good luck,
Victor
P.S.
My W163 270 CDI is 2003 year facelift one. I am not a native English speaker, sorry if something what I wrote is difficult to understand.

Dtpetrov

Thanks for the full information. For the auto transmission i also change the oil, i buy the car with 260 000 km. After this the problem was still there but not so big surge. In that time i also change the potentiometer and i was not sure what of this made some change. If im sure that the reason is torq converter i will change it, but i have gone to the auto transmison shop and they told me that the problem is in the engine. Im going crazy because this is a very comfortable car, but with this kind of problem its very anoying, and i dont know what else i can do. Today before your post i was thinking to change the vpc solenoid vacuum for the turbo and egr, but after your post im not sure anymore. I will keep going to solve the problem, if i managed to do it ill write you immediately. Now im thinking for new ZF torq conv.

Dtpetrov

And i have to tell you also that when surge begins, if i press the throttle pedal more, the surge dissapears. Also the auto trans shifts down if needed without a problem. I begin to thing that may be theres nothing else left than the converter.
May be its not important, but my potentiometer is also second hand. Is there any chance when its not new, to have the same problem and to behave the same way. Is it possible potentiometer to lie the computer of the car and to make this surge problem. Mine potentio is not tested before i buy it.if i have to i will buy brand new.

Winme

Hi Dtpetrov
You said: "And I have to tell you also that when surge begins, if I press the throttle pedal more, the surge disappears" - exactly as in my case! like you are driving my car !
When I said the transmission does not downshift, I meant that by the moment the surge starts (you go uphill) my expectation is the control module should downshift the gear - let's say go to fourth. But it does not. Like you are riding manual gearbox and you are lazy to shift the gear when the engine can not overcome an increased load.
Same thing happens if you have set the cruise control as well - with cruise control engaged the potentiometer stays at zero. This makes me think that throttle sensor (potentiometer) can not cause surging problem. Second hand potentiometers are cheap which means they are not vulnerable pieces and folks do not need them. Anyway if the potentiometer was faulty, you would definitely have a respective fault code. I would not waste money one a new potentiometer.
Later I will tray to upload a video which shows how my tachometer arrow shuttles.
Victor

Dtpetrov

Hi Victor. This information opens my eyes. I didnt know that the potentiometer is at zero when car is on cruise control. Because when my cruise is on the problem is the same. Today i will buy one vacuum solenoid for the EGR. Mine make some strange noises and rattles when car is working. I will try that too. Next month i will go to try star diagnosis but on the road to see how sensors etc. works on load and i hope to find the cure. Interesting thing is that sometimes when with 120 km on the highway the car doesnt make all the problems just feels like missfire on the petrol engine. I cant exactly explain but feels like shut the engine off for a second and then turn it on. This happens very quick. That make me think that the problem is in the engine.
For the downshifting you are right- mine also began to drop the rpm on load but dont downshift by herself and i have push the pedal down.
Best regards

Dtpetrov

Tried what i was planning. Nothing worked and problem got worse. I havent drive the car with more than 120 km h. Today i tried to drive with 140, and epc light turned on and cuts the engine. After this car starts normally, but after next acceleration to 140 enegine cuts off immidiately. Going to star next week.
Solved. Change na common rail pressure valve.

Dtpetrov

After a lot diagnosis, from autoshop think that the problem is in the torque conv. The clutches are worn out and when they slip the problem is visible like surging and vibration. I will change the cinv but after winter, and write here again the results.

Tschuss_Bill

Check the valve body too. There are two screens that can clog up with clutch material. Worth getting valve updates while things are apart.

Dtpetrov

Yes they told me that the whole AT will be dissasembled and look inside. If there is something not good they will change that too.

Winme

Hi everyone,
As a thread starter I think I must tell you that I resolved my "surging at 110 km/h" problem:

Few moth ago I was on the road about three hours and I stopped for a coffee. After the coffee break I was not able to restart engine (and this was the first time that happened to my ML 270cdi) - battery was nearly flat when finally the engine fired up and I had a crazy driving to city - I was nearly late.
I had to leave my car to BOSCH service - engine bay was dampened with diesel fuel and full of diesel mist. I was told the serpentine belt had cut a diesel fuel plastic tube under the high pressure pump - yes, I replaced the serpentine belt few days earlier to this incident ! OM 612 owners know how this happens.

I had some conversation with BOSCH service technicians about engine surges and a young guy suggested to replace a camshaft sensor (I never tried it in my endless trials to resolve surging problem), he told this sensor is a tricky one and does not manifest itself - in the majority of cases does not trigger malfunction codes, does not cause start-up problems when cold, etc.
I replaced the camshaft sensor and I am happy - power has come back to my engine. On uphill at 120km/h RPMs go down steadily to about 2450/2400 and my Automatic Transmission downshifts! I have been monitoring my car behaviour for more than three months and now I can say for sure that camshaft sensor replacement worked to me.

I hope Dtpetrov did not split apart his transmission and he has a chance to try camshaft sensor replacement - I think an used one does not cost more than 50 USD, this would be much cheaper than transmission rebuild. I was told engine control module sends torque/power output data to transmission control module, if there is something abnormal with engine, the transmission does not perform normally as well.

From some other treads I remember an American guy owning a Sprinter van (manual transmission) being very disappointed of the van due to same surging problem - he was sure his engine was to its power output top when surges were appearing. And he was right - seems, with faulty camshaft sensor engine is running with alternative programme and is not capable to give full rated power. I do not know why all this can not be captured with diagnostic equipment - CDI 1 and CDI2 software may have some "white spots".

Good luck to everybody!
Victor

Dtpetrov

Thank you Victor, i hope you will be right. I didnt split AT yet, because its still winter where i live, and i wanted winter to end. I will try new camshaft sensor this week and after weekend test i will write down what happend. Here in Bulgaria, the price for AT rebuilt, including torque converter change is about 1500 dollars, but if you are right and the problem is not the transmission i will waste this money. Greetings from Bulgaria.

Dtpetrov

Hi guys. I cheked AT in shop they told me that the peoblem is not there. I called the previous owner and he told me that he removed the swirl flaps, but he did that only from the manifold, but not with software. Is it possible with removed swirl flaps without make a delete with star diagnosis to make this surgung because the engine getting too much air necause the computer of the car think SF are closed in some moment. Friday i have an appointment to specialist to test it on the road and i will test the camshaft sensor too.
I've read somewhere that with removing swirls you have to delete actuator motor and the EGR too, because the egr with removed swirls also makes a problem with too much air for the engine. If someone did some of this give some information how to do it right. Thanks

Dtpetrov

Hi guys, its been a while but i had a lot of work, didnt have time for car. After 2 hours of star diagnostics they told me the egr is stuck open and the second injector is leaking fuel. First i change the egr. After 20 min driving the car was like new. After this 20 min ot high way the surging got worse, which is strange. Is there any connection according to you with the temperature in the oil in AT. The oil was changed 20k km ago.
I will change the second injector but i dont think the problem is there.
Also the machanic said that there is a lot of oil from the turbo. A can hear the turbo, it works but the oil leak can cause the problem in some steady rpms maybe.

joinedtrill

Hi folks, I'll just add some experience of my own. Interesting to read about the cam sensor, i wonder if that's a contributing issue. The issue I'm tracking is valve failure in my trans. I have a serious "false neutral" on 3-4 shift, above 80 Celsius and lately, i have a flare at above 100kph. The test / cure has been to hold 4th until 100 and keep it there for a minute or so, especially if it's after a climb and on the level. I then manually shift to 5th (D) and the flare is gone, for some time. I always attributed this to building enough pressure in the shift hydraulics to hold the "torque converter lockup damper valve" in the correct position. Adding to that thought, i wonder if holding the revs in 4th, cleans the signal from the cam position sensor allowing it to behave more consistently when shifting to 5th (D). Thanks for sharing everyone. Good motoring.